In recent years, an image capturing device of a compact and slim configuration has come to be mounted on a portable terminal as an electric device of compact and slim configuration such as a cellular mobile telephone and PDA (Personal Digital Assistant). This has resulted in mutual exchange of both audio information and visual information with a remote place. The image capturing element used in the image capturing device is a solid image capturing element such as a CCD (Charge Coupled Device) type image sensor and CMOS (Complementary Metal-Oxide Semiconductor) type image sensor. Further, resin lenses that can be mass-produced at a reduced cost have come to be employed as image capturing lenses for forming a subject image on an image capturing element because of lower costs thereof.
Further, in the cellular mobile telephone, the image capturing lens and image capturing device are mounted on the printed circuit board in recent years. A reflow soldering process is used to mount the image capturing lens and image capturing device on the printed circuit board. This process will be referred to as reflow process in the following description. In the reflow process, solder is placed in advance at the position wherein electronic components are arranged on the printed circuit board and the electronic components are arranged there. The heat is applied to dissolve the solder. After that, the solder is cooled and the electronic components are mounted on the printed circuit board. The electronic components are automatically mounted in a furnace for reflow process. Use of this reflow process has reduced the costs for mounting the components on the printed circuit board and ensures the product quality to be maintained at a predetermined level.
In this connection, one of the methods of producing a lens and optical system is a replica method wherein a plurality of lenses are formed simultaneously on one lens plate. The replica method permits the lens portion to be made of resin. However, in the resin lens, a change in the refractive index with respect to temperature change is generally negative. Accordingly, serious defocusing from the design level is caused by the operation temperature and the performance is deteriorated. Further, the linear expansion coefficient of the resin lens is generally greater than that of glass. Thus, the paraxial radius of the lens portion is increased by the free thermal expansion caused by temperature rise. This will result in defocusing, hence, deterioration in performances.
Regarding this point, the Patent Literature 1 discloses that, when a resin lens is formed on the surface of a parallel plane glass plate, excellent aberration performances can be provided by a smaller difference in refractive index between the parallel plane glass plate and resin lens.    Patent Literature Japanese Patent Publication No. 3926380